The present invention relates to an improvement of a lead acid storage battery.
The lead acid storage battery is generally a storage battery using lead dioxide in the positive electrode and lead in the negative electrode as active materials, and dilute sulfuric acid as an electrolyte. And it is the secondary battery most widely used for portable equipment, motor vehicles, industrial applications, and recently for electric vehicles. As a method for producing this lead acid storage battery, there have been historically known paste process, clad process, and Tudor process. Recently, a method of kneading and filling a special resin and lead powder in a lead or lead alloy current collector has been known.
In the battery configuration, too, a wide variety of forms are now put to practical uses from the conventional configuration using an abundant amount of electrolyte to a sealed-type battery which is so limited that the electrolyte is absorbed in a glass mat and oxygen evolving from the positive electrode during overcharging is ionized on the negative electrode.
In any application, size and weight reduction is a common subject, and the utilization improvement of the active material is an endless proposition. However, the fact is that, in the unitization of the active material, the lead acid storage battery is limited to a low level as compared with other battery systems. Recently in particular, the low utilization at a high rate discharge has been a block to further widening applications.
It is known that the utilization even at a low rate discharge of not higher than 0.1 C by the theoretical filling capacity standard is generally at most 50-55% at the positive electrode and 60% or so at the negative electrode on the theoretical filling capacity and drops below a level of 20% at a high rate discharge exceeding 5 C. Generally, the theoretical filling amount of the negative electrode is large as compared with the positive electrode, and the utilization of the positive electrode determines the battery capacity in many cases.
In a long history, much research has been done to solve the problem of low utilization. But no means to essentially improve the utilization has been born. It is considered that the factor to determine the utilization at a high rate discharge is the diffusion or supply of sulfuric acid. To facilitate this supply of sulfuric acid, a method of adding a surfactant or the like to the electrolyte has been tried without practical results, and thus no good way to improve the utilization has been found out except for forming a configuration suited for the diffusion of sulfuric acid. In other words, it has been thought that once a structure is decided upon, there is no means to raise the utilization of the active material.